Art of removing lead from tubes and other articles



Patented July 18, 1933 UNITED STATES PATENT; OFFICE CHARLES L. MANTELL, OF BROOKLYN, NEW YORK, ASSIGNOR TO DUDZEELE CORPORA- TION OF AMERICA, OF NEW YORK, N. Y., A CORPORATION OF DELAWARE ART OF REMOVING LEAD FROM TUBES AND OTHER ARTICLES NoJJrawing. Application filed December 12, 1928, Serial No. 325,643. Renewed January 19, 1933.

My invention relates to the art of removing lead coating from tubes, or other articles, such as terne plate, scrap, etc., and includes both a process and the novel deleading baths used therein.

Broadly, my invention consists in removing the lead coating by subjecting it (as by immersion) to a solution which has an acid reaction on the lead, which is converted to such form or condition that it is freed from the underlying body (usually of steel or iron), the solution being so composed and the process so conducted that the acid action upon the body surface is slight or negligible.

Heretofore, so far as I-am aware, lead has been removed from articles only by electrolytic action; probably this is because it has been considered impossible or impracticable to remove a lead coating by acid treatment without objectionable acid attack upon the coated object. This undesired result I avoid by 'means explained below, and I am therefore able to effectively and economically remove lead coating by purely chemical action,

and to dispense with the electrolytic method,

which is relatively expensive, slow and annoying for reasons known to skilled persons.

One specific application of the invention is in connection with a known process of drawing tubes and fabrication of metal in which lead coatings are employed to prevent or lessen the effect of cold working. With lead coated tubes, a number of drawings or rollings can be made before annealing is necessary. In many cases it is necessary to remove the lead without afi'ecting the tube surfaces, or affecting them only within commerciallv allowable limits.

Lead is one of the best known metals employed as a material of construction for corrosion resistance. Its use in the manufacture of sulphuric acid and in the chemical industries is well known. It is quite resistant to most forms of chemical attack.

The tubes or fabricated shapes to be deleaded are first cleaned in a solution of an alkali, such as sodium hydroxide, at temperatures preferably near the boiling point; or heated aqueous solutions of so-called commercial cleaners may be employed, or alkali solutions with emulsifying agents such as sulphonated oils, and detergents of various sorts (as sodium carbonate,:phosphates, etc.)

After cleaning, the tubes or other articles to be deleaded are immersed in the deleading solution in the general manner and method employed in the pickling of rolled or drawn steel articles.

By study and experiment I have demonstrated that saturated aqueous solutions of sodium chloride (common salt) with the addition of from 0.5% to 10% sulphuric acid, or acid sulphates, are very effective lead removal agents.

I have also found that solutions contain ing appreciable amounts of chlorides and nitrates, made acid in character, or acquiring an acid reaction as the result of the nature of the salts used, can be employed as lead removal agents. Examples are l to 10% ferric chloride and 2 to 10% sodium nitrate in combination; or 1 to 10% sodium chloride, acidified by hydrochloric acid, and 2 to 10% sodium nitrate.

Solutions containin soluble sulphates, nitrates, acetates in com ination are also effective. As an example a successful solution is the following: 5% sodium acid sulphate (NaHSO 2 to 5% sodium acetate (NaC I-I O 2 to 5% sodium nitrate (NaNO3) or saltpeter.

Solutions containing soluble sulphates, nitrates, acetates, in combination, as well as additions of sulphuric acid, function readily as lead removal agents. An example is 5% sodium nitrate, plus the addition of 1 to 10% sulphuric acid.

One of the most effective and best adapted solutions for commercial work I have found to consist of soluble sulphates, nitrates, acetates, chlorides in combination, plus the addition of sulphuric acid. It is desired that the solution work and remove the lead without having marked effect on the ferrous metal or alloy composing the main bulk of the fabricated article. As an example of a commercial solution, successful results have been produced With 5 sodium acid sulphate (NaHSOJ 2 to 5% sodium nitrate (NaNO 2 to 5% sodium acetate (NaC H O saturated sodium chloride (NaCl), plus 1 to 10% sulphuric acid. Considcrable variation is permissible in the proportions of the various constituents. It is believed that the sulphuric acid acts on the nitrates and acetates to liberate the correspondilig acids, both of which attack lead; that the sulphuric acid acts on the sodium chloride to liberate hydrochloric acid which attacks lead, but whose'attack would ordinarily stop as the result of the formation of lead chloride, which is only slightly soluble in the cold but very soluble in hot water or solutions, and readily soluble in saturated solutions of sodium chloride, or solutions containing appreciable concentrations of sodium chloride. In addition, it is believed that small amounts of aqua regia, well known in the arts and to the working chemist, are formed by the combination of the nitric and hydrochloric acids liberated by the action of sulphuric acid on the corresponding salts. Aqua regia corrodes and attacks lead.

In some of the baths the lead removal is wholly chemical by solution; in others, it may be partially mechanical (as the result of attack on the iron through holes in the lead coating, the gases resulting from the attack lifting the lead and flaking it off) and partially chemical. In those solutions containing nitrates it is believed that the nitrates somewhat passivate the iron or iron alloy, and render it more resistant to attack.

Excellent results have been obtained in commercial practice on tubes which have been deleaded by the use of the solutions as described, operated at temperatures from 180 F. to the boiling point of the solutions, followed by washing in water, and a short pickling in a 2 to 5% sulphuric acid solution containing an inhibitor, the use of which is now well known in the arts, such as, for example, the commercial products known as rodine, goulac, and similar cellulose and paper pulp products. Excellent surfaces have been produced in this manner, as well as by pickling immediately following deleading, without washing in water. The time necessary for deleading is a function of the size of the article to be deleaded, the thickness of coating, and the surface finish desired.

I claim:

The method of removing lead from lead coated articles, which includes the step of subjecting them to treatment in a bath containing soluble sulphates. acetates, nitrates, and chloride ions of a concentration corresponding to that of a saturated solution of sodium chloride, and sulphuric acid, the bath having a temperature of about 180.

CHARLES L. MANTELL. 

